2x4+6=(6-4x6)
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L
2
HP
2 tháng 7 2016
\(D=\frac{6}{2x4}+\frac{6}{4x6}+\frac{6}{6x8}+....+\frac{6}{48x50}\)
\(=\frac{6}{2}x\left(\frac{2}{2x4}+\frac{2}{4x6}+\frac{2}{6x8}+....+\frac{2}{48x50}\right)\)
\(=3x\left(\frac{1}{2}-\frac{1}{4}+\frac{1}{4}-\frac{1}{6}+\frac{1}{6}-\frac{1}{8}+....+\frac{1}{48}-\frac{1}{50}\right)\)
\(=3x\left(\frac{1}{2}-\frac{1}{50}\right)=3x\frac{12}{25}=\frac{36}{25}\)
Vậy D=36/25
2 tháng 7 2016
D=6/2x4 + 6/4x6 + 6/6x8 + ...+ 6 /48 x50
D=3 x (2/2x4 + 2/4x6 + 2/6x8 + ...+ 2 /48 x50)
D= 3x (1/2 - 1/4 + 1/4 - 1/6 + 1/6-1/8 + ... + 1/48 - 1/50)
D= 3 x (1/2 - 1/50)
D= 3 x 12/25
D= 36/25
TH
3
TH
5 tháng 5 2019
\(\frac{6}{2x4}+\frac{6}{4x6}+\frac{6}{6x8}+...+\frac{6}{98x100}\)
\(=3x\left(\frac{2}{2x4}+\frac{2}{4x6}+\frac{2}{6x8}+...+\frac{2}{98x100}\right)\)
\(=3x\left(\frac{1}{2}-\frac{1}{4}+\frac{1}{4}-\frac{1}{6}+...+\frac{1}{98}-\frac{1}{100}\right)\)
\(=3x\left(\frac{1}{2}-\frac{1}{100}\right)=3x\left(\frac{50}{100}-\frac{1}{100}\right)=3x\frac{49}{100}\)
\(=\frac{147}{100}\)
5 tháng 5 2019
\(\frac{6}{2\cdot4}+\frac{6}{4\cdot6}+\frac{6}{6\cdot8}+...+\frac{6}{98\cdot100}\)
=\(\frac{3\cdot2}{2\cdot4}+\frac{3\cdot2}{4\cdot6}+\frac{3\cdot2}{6\cdot8}+...+\frac{3\cdot2}{98\cdot100}\)
=\(\text{}3\cdot\left(\frac{2}{2\cdot4}+\frac{2}{4\cdot6}+\frac{2}{6\cdot8}+...+\frac{2}{98\cdot100}\right)\)
=\(\text{}3\cdot\left(\frac{1}{2}-\frac{1}{4}+\frac{1}{6}-\frac{1}{8}+...+\frac{1}{98}-\frac{1}{100}\right)\)
=\(\text{}3\cdot\left(\frac{1}{2}-\frac{1}{100}\right)\)
=\(\text{}3\cdot\frac{49}{100}=\frac{147}{100}\)
ML
6 tháng 8 2017
\(a,\frac{4}{2.4}+\frac{4}{4.6}+\frac{4}{6.8}+....+\frac{4}{16.18}+\frac{4}{18.20}\)
\(=\frac{4}{2}\left(\frac{1}{2}-\frac{1}{4}+\frac{1}{4}-\frac{1}{6}+\frac{1}{6}-\frac{1}{8}+...+\frac{1}{18}-\frac{1}{20}\right)\)
\(=2\left(\frac{1}{2}-\frac{1}{20}\right)\)
\(=2.\frac{9}{20}\)
\(=\frac{9}{10}\)
\(b,\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+...+\frac{1}{90}\)
\(=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{9.10}\)
\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{9}-\frac{1}{10}\)
\(=1-\frac{1}{10}\)
\(=\frac{9}{10}\)
21 tháng 10 2021
\(A=\dfrac{1}{1\cdot2}+\dfrac{1}{2\cdot3}+...+\dfrac{1}{49\cdot50}\)
\(=1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+...+\dfrac{1}{49}-\dfrac{1}{50}\)
\(=\dfrac{49}{50}< 1\)
12 tháng 3 2022
=1(2+1)+2(3+1)+3(4+1)+...+100(101+1)
=1.2+1+2.3+2+3.4+3+...+100.101+100
=(1.2+2.3+3.4+..+100.101)+(1+2+3+...+100)
=333300+5000
=338300
WR
8 tháng 7 2015
2[1/2X4+1/4X6+1/6X8+...+1/Xx(X+2)]=11/45x2
2/2x4+2/4x6+2/6x8+....+2/Xx(X+2)=22/45
1/2-1/4+1/4-1/6+1/6-1/8+...+1/x-1/x+2=22/45
1/2-1/x+2=22/45
1/x+2=1/2-22/45
1/x+2=1/90
=>x+2=90
=>x=88
vậy x=88
8 tháng 7 2015
\(\frac{1}{2.4}+\frac{1}{4.6}+\frac{1}{6.8}+...+\frac{1}{x\left(x+2\right)}=\frac{11}{45}\)
\(\Rightarrow\frac{2}{2.4}+\frac{2}{4.6}+\frac{2}{6.8}+...+\frac{2}{x\left(x+2\right)}=\frac{22}{45}\)
\(\Rightarrow\frac{1}{2}-\frac{1}{4}+\frac{1}{4}-\frac{1}{6}+\frac{1}{6}-\frac{1}{8}+...+\frac{1}{x}-\frac{1}{x+2}=\frac{22}{45}\)
\(\Rightarrow\frac{1}{2}-\frac{1}{x+2}=\frac{22}{45}\)
\(\Rightarrow\frac{1}{x+2}=\frac{1}{2}-\frac{22}{45}\)
\(\Rightarrow\frac{1}{x+2}=\frac{1}{90}\)
=>x+2=90
=>x=90-2
=>x=88
vậy x=88
NT
0
PG
0
TP
1
27 tháng 8 2017
S=(2+98)*(4+6)+...+100+100+102
100*10+....+100+100*102
=224400
2x^4+6=-18
2x^4=-18-6
2x^4=-24
x^4=-12
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